Re: [RFC v2 07/11] tap: support tx through vhost

[Stefano Brivio <sbrivio@redhat.com>]

Silly comments only:

On Thu, 24 Jul 2025 10:24:39 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Jul 09, 2025 at 07:47:44PM +0200, Eugenio Pérez wrote:
> > No users enable vhost right now, just defining the functions.
> > 
> > The use of virtqueue is similar than in rx case.  fills the descriptor
> > table with packet data it wants to send to the namespace.  Each
> > descriptor points to a buffer in memory, with an address and a length.
> > The number of descriptors is again defined by VHOST_NDESCS.  
> 
> Does the number of descriptors have to be equal for the Tx and Rx
> queues?  For Rx, the number of descriptors is basically determined by
> how many frames we can fit in pkt_buf.  That doesn't really apply to
> the Tx path though, it would be more natural to define the number of
> Tx descriptors independently.
> 
> > Afterwards it writes the descriptor index into the avail->ring[] array,
> > then increments avail->idx to make it visible to the kernel, then kicks
> > the virtqueue 1 event fd.
> > 
> > When the kernel does not need the buffer anymore it writes its id into
> > the used_ring->ring[], and increments used_ring->idx.  Normally, the
> > kernel also notifies pasta through call eventfd of the virtqueue 1.
> > But we don't monitor the eventfd.  Instead, we check if we can reuse the
> > buffers or not just when we produce, making the code simpler and more
> > performant.  
> 
> Oh, that's pretty neat.
> 
> Nit: s/performant/performent/

Actually, "performent" (which I had never heard before) seems to be an
archaic term for "performance":

  https://www.oed.com/dictionary/performent_n

whereas "performant":

  https://en.wiktionary.org/wiki/performant

seems to be fitting here (as much as I'd favour "efficient" instead,
because it actually sounds like a real word ;)).

-- 
Stefano